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Chapter 30
Microbial Interactions
(미생물의 상호작용)
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공생 (Symbiosis)
• 상리공생 (mutualism) – 서로 이익
• 협동관계 (cooperation) – 서로 분리되는 죽
음
• 편리공생 (commensalism) – 한쪽만 이익
• 포식작용 (predation)
• 기생 (parasitism) – 한쪽은 이익, 한쪽은 해
• 편해작용 (amensalism) ‐ 한쪽만 해
• 경쟁 (competition)
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노토바이오틱 동물
• 무균상태 (germ‐free)
• 노토바이오틱 (gnotobiotic)
– 모든 미생물을 알고 있는 상태
– 미생물학적 조사가 가능한 무균상태
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Normal Microbiota of the Human Body
• Normal microbiota (고유미생물상), microflora (미생물총), or normal flora (정상
세균총) – Microbes regularly found at an anatomical site
• Relationship begins at birth • Varies with environment and food source
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Reasons to Study Normal Human Microbiota
• To gain insight into possible infections resulting from injury
• To understand causes and consequences of overgrowth of microbes normally absent from a body site
• To increase awareness of role played by indigenous microbe in stimulating immune response
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기회감염 (opportunistic infection)
• 기회감염 미생물 (opportunistic microorganism)
• 기회감염 병원체 (opportunistic pathogen)
• 약화된 숙주 (compromised host)
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Chapter 31
감염과 병원성
(Infection and Pathogenicity)
Host, parasites, and infection
• Host (숙주)
– Larger organism that supports the survival and growth of a smaller organism
• Parasites (기생생물)
– Organisms that live on or within a host organism – Metabolically dependent on the host
– Any organism that cause disease
• Infection (감염) – A parasite growing and multiplying within or on a host
Pathogen and pathogenicity
• Pathogen (병원균)
– Any parasitic organism that causes infectious disease
– Primary pathogen (1차 병원체) • Causes disease by direct interaction with healthy host
– Opportunistic pathogen (기회감염 병원체) • Causes disease only when it has gained access to other tissue sites or host is immunocompromised • Pathogenicity (병원성)
– Ability of parasite to cause disease
Active versus latent infection
• Active infection (활성 감염)
– Transmission of the organism occurs – Symptoms are present within the host
• Latent infection (잠복 감염)
– No transmission of the organism occurs – No symptoms are present within the host
– Herpesvirus infection, tuberculosis and leprosy
Factors Impacting Outcome of Host‐
Parasite Relationships
• Number of organisms present (개체수)
• The degree of virulence of pathogen (독성인자)
• Host’s defenses or degree of resistance (숙주 저
항성)
The Infectious Disease Process
• Infectious disease (감염성 질병)
– Infection with viruses, bacteria, fungi, protozoa (원생동물), and helminths (기생충)
• Signs (징조)
– Objective changes in body that can be directly observed
• Symptoms (증상)
– Subjective changes experienced by patient
• Disease syndrome
– Set of characteristic signs and symptoms
Course of Infectious Disease
• Incubation period (잠복기)
– Period after pathogen entry but before signs and symptoms appear
• Prodromal stage (전구기)
– Onset of signs and symptoms
– Not clear enough for diagnosis
• Period of illness (질병기)
– Disease is most severe and has characteristic signs and symptoms
• Convalescent period (회복기)
– Signs and symptoms begin to disappear
The Source or Reservoir • Source (감염원)
– Location from which pathogen is transmitted to host
• Period of infectivity (감염기간)
– Time during which source is infectious or is disseminating the organism
• Reservoir (보유체)
– Site or natural environmental location in which pathogen is normally found
• Carrier (보균자)
– Infected hosts who are potential sources of infection for others
Pathogen Transmission
(병원체의 전파)
• Transmission alone not enough for infection to occur
• Tropism (친화성) ‐ pathogen must make contact with appropriate host tissue
– Determined by specific cell surface receptors
– Hepatitis viruses only infect liver
인수공통전염병
• 인수공통전염병 (zoonosis)
• 동물에서 사람에게 감염
• 매개자 (vector)
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Pathogen Transmission
• Four main modes of transmission
– Airborne (공기매개)
– Contact (접촉성)
– Vehicle (운반체)
– Vector borne (매개자)
Growth of Pathogen
• Extracellular pathogens (세포외 병원체)
– Grow outside cells in blood, tissue fluids
• Intracellular pathogens (세포내 병원체)
– Grow and multiply within cells
– Facultative (조건부) intracellular pathogens
• Grow within or outside cells
– Obligate (절대) intracellular pathogens
• Only grow when inside cells
Host Susceptibility (감수성)
• Two main factors
– Defense mechanisms of host (숙주 방어기전)
– Pathogenicity of pathogen (병원성)
• Nutrition, genetic predisposition, and stress also play a role in host susceptibility to infection
Exiting the Host (숙주 탈출)
• Must occur if microbe is to be perpetuated
• Active escape (능동적 탈출)
– Movement of pathogen to portal of exit
• Passive escape (수동적 탈출)
– Excretion in feces, urine, droplets, blood, saliva, or desquamated (벗겨지는) cells
Virulence (독성)
• Degree or intensity of pathogenicity • Virulence factors (독성인자)
– Determine the degree to which the pathogen causes damage, invasion, infectivity
• Determined by characteristics of the pathogen
– Adherence (부착) and colonization (집락화)
– Invasion (침입)
Adherence and Colonization
• Adherence (부착)
– Mediated by special molecules or structures called adhesins
• Colonization (집락화)
– Establishment of a site of microbial reproduction on or within host
Invasion (침입)
• Infectivity (감염성)
– Ability of the organism to establish a discrete, focal point of infection
• Invasiveness (침입성)
– Ability of organism to spread to adjacent or other tissues
• Penetration of host’s mucous membranes (
점막) or epithelium (상피) can be active or passive
Active Invasion (능동 침입)
• Lytic substances (용해성 물질)
– Attack the extracellular matrix and basement membranes of integuments (외피) and intestinal linings
– Degrade carbohydrate‐protein complexes between cells
– Disrupt host cell surface
Passive Invasion (수동 침입)
• Penetration through skin lesions, insect bites, wounds
• Once below mucous membrane (점막), bacterium can spread to deeper tissues
• Involves production of specific products and/or enzymes that promote spreading
Invasion (침입)
• Once in circulatory system, microbes have access to all organs and systems
– Bacteremia (균혈증) – presence of viable bacteria in the blood
– Viremia (바이러스혈증) ‐ spread of viruses in the blood and hence gain access to the rest of body
– Septicemia or sepsis (패혈증) – bacteria, other pathogens, or their toxins in the blood Resisting Host Defenses
• Most microbes eliminated before they can cause disease due to immune system
• Successful pathogen evades immune system • Numerous mechanisms for both viral and bacterial pathogens
Mechanisms Resisting Host Defenses 1
• Infection of immune system cells, diminishing their function
• Fuse with adjacent cells to prevent exposure to antimicrobial proteins in host • Capsules and specialized surface proteins prevent phagocytosis
• Production of decoy (유인) proteins to bind available neutralizing antibodies
Mechanisms Resisting Host Defenses 2
• Mutations (돌연변이) change antigenic sites or alter expression of antigens through downregulation of phase variation
• Produce substances that resemble host tissue
• Produce proteases that degrade host proteins • Special proteins that interfere with host defenses
Toxigenicity
• Toxigenicity (독소생성력)
– Ability to produce toxins
• Intoxications (중독)
– Diseases that result from entry of a specific preformed toxin into host
• Toxin (독소)
– Specific substance that damages host
• Toxemia (중독증)
– Condition caused by toxins in the blood of host
Exotoxins (외독소)
• Soluble, heat‐labile (열에 불안정한) proteins
• Usually released into the surroundings as bacterial pathogen grows
• Most exotoxin producers are gram‐positive
• Often travel from site of infection to other tissues or cells where they exert their effects
Exotoxins (외독소)
• Usually synthesized by specific bacteria that have toxin genes in their plasmids or prophage DNA
• Among the most lethal substances known are highly immunogenic (면역반응유도)
• Can stimulate production of neutralizing antibodies (중화항체) or antitoxins (항독소)
• Can be chemically inactivated to form immunogenic toxoids (변성독소) to be used as vaccine
Types of Exotoxins
(외독소의 종류)
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•
•
•
AB exotoxins
Specific host site exotoxins
Membrane‐disrupting exotoxins
Superantigens
AB Exotoxins
• Composed of two subunits
– A subunit – responsible for toxic effect
– B subunit – binds to specific target cell
• Mechanisms of action
– Protein synthesis inhibition (ADP ribosylation of EF‐2 factor)
– Ribonuclease activity
– Signal transduction interference
– Blocking neurotransmitters
Specific Host Site Exotoxins
• Can be AB toxins
• Neurotoxins (신경독소)
– Target nerve tissue
– Botulinum and pertussis toxins
• Enterotoxins (장독소)
– Target intestinal mucosa
– Cholera and E.coli toxins
• Cytotoxins (세포독소)
– Target general tissues
– Diphtheria and Shiga toxins
Membrane‐Disrupting Exotoxins
(막파괴 외독소)
• Do not have separable A and B subunits
• Pore‐forming exotoxins (통로형성 외독소)
• Phospholipases (인지질 분해효소)
Pore‐Forming Exotoxins
• Leukocidins (백혈구 독소)
– Kill phagocytic leukocytes
• Hemolysins (용혈소)
– Kill erythrocytes, leukocytes, and many other cells
Phospholipase Enzymes
• A second subtype of membrane‐disrupting toxins
• Remove charged head group from lipid part of phospholipids in host‐cell plasma membranes • Membrane destabilizes, cell lyses, and dies
• Clostridium perfringens, 가스괴저균
Superantigens
• Stimulate ~30% of T cells of the immune system
• Causes the T cells to overexpress and release cytokines
• Results in failure of multiple host organs allowing time for the microbe to disseminate
• Staphylococcal enterotoxin B (포도상구균
장독소 B, SEB)
Endotoxins (내독소)
• Bacterial cell wall lipopolysaccharide (LPS, 지질다당체) in gram‐negative cell wall can be toxic to specific hosts
• Bound to bacterium and released when organism lyses and some is also released during multiplication • Toxic component is the lipid portion, lipid A
Lipopolysaccharide (지질다당체, LPS)
Endotoxins (내독소)
•
•
•
•
•
Heat‐stable (열에 안정)
Toxic (nanogram amounts)
Weakly immunogenic
Generally similar, despite source
Cause general system effects
– Fever, weakness, diarrhea, inflammation, intestinal hemorrhage, and fibrinolysis (섬유소
용해), the enzymatic breakdown of fibrin, the major protein component of blood clots
Endotoxins (내독소)
• Bring about these effects indirectly
• Endotoxin interacts with host molecules and cells, activating host systems
• Activation of coagulation (응고), complement (보체), fibrinolytic (섬유소용
해), and kininogen system
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Endotoxins (내독소)
• Interaction with macrophages  release of endogenous pyrogen (내인성 발열인자) such as IL‐1 (interleukin‐1), which induces fever)
• Binding to LPS‐binding protein  release of cytokines including tumor necrosis factor (TNF) and others lead to septic shock (패혈
성 쇼크)
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외독소와 내독소의특징
Mycotoxins (진균독소)
• Secondary metabolites of fungi
– Common contaminants of food crops
– Aspergillus flavus and A. parasiticus produce carcinogenic aflatoxin
– Stachybotrys produce tissue‐damaging satratoxins
– Claviceps purpurea (ergot) produce hallucinogen lysergic acid
Measuring Virulence
• Lethal dose 50 (LD50)
– Dose that kills 50% of experimental animals within a specified period
• Cytopathology – cellular changes
• Examining virulence factors and their release